Oxo-titanylphthalocyanine crystal, method for producing the same, and electrophotographic photoreceptor

ABSTRACT

The invention provides an oxo-titanylphthalocyanine crystal which is stable, is superior in dispersibility in a photoreceptive layer and efficiently contributes to improvements in sensitivity and charge retention rate of an electrophotographic photoreceptor when it is used as a charge generating agent, a method for producing the oxo-titanylphthalocyanine crystal, and an electrophotographic photoreceptor. The oxo-titanylphthalocyanine crystal has predetermined optical characteristics and thermal properties and is produced by a production method including the following steps (a) to (d): (a) a step of dissolving a crude oxo-titanylphthalocyanine crystal in an acid to obtain an oxo-titanylphthalocyanine solution; (b) a step of adding the oxo-titanylphthalocyanine solution dropwise in a poor solvent to obtain a wet cake; (c) a step of washing the wet cake with an alcohol having 1 to 4 carbon atoms; and (d) a step of stirring the washed wet cake under heating in a nonaqueous solvent to obtain an oxo-titanylphthalocyanine crystal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an oxo-titanylphthalocyanine crystalformed from an oxo-titanylphthalocyanine compound, a method forproducing the oxo-titanylphthalocyanine crystal, and anelectrophotographic photoreceptor. In particular, the invention relatesto an oxo-titanylphthalocyanine crystal which is stable, is superior indispersibility in a photoreceptive layer and efficiently contributes toimprovements in sensitivity and charge retention rate in enelectrophotographic photoreceptor, a method for producing theoxo-titanylphthalocyanine crystal, and an electrophotographicphotoreceptor.

2. Description of the Related Art

Generally, as electrophotographic photoreceptors for use inelectrophotographic devices such as copying machines and laser printers,many organic photoreceptors have been used to cope with, for example,demands for low costs and a resistance to environmental pollution. Ascharge generating agents for use in such organic photoreceptors, widelyused are phthalocyanine type pigments sensitive to infrared ornear-infrared light emitted from a semiconductor laser, infrared LED orthe like.

Also, it is known that such phthalocyanine type pigments includenon-metal phthalocyanine compounds, copper phthalocyanine compounds,titanylphthalocyanine compounds and the like depending on their chemicalstructures, and also, each phthalocyanine compound can take variouscrystal forms by a difference in production conditions.

It is known that when an electrophotographic photoreceptor usingoxo-titanylphthalocyanine compound having a Y-type crystal structure asthe charge generating agent is produced in the presence of many types ofphthalocyanine compound crystals differing in crystal type, electriccharacteristics in the electrophotographic photoreceptor are moreimproved as compared with the case of using oxo-titanylphthalocyaninehaving other crystal types.

With regard to the Y-type oxo-titanylphthalocyanine crystal, a methodfor producing an oxo-titanylphthalocyanine crystal having a maximumdiffraction peak at a Bragg angle (2θ±0.2°)=27.3° with respect to CuKαray in an X-ray diffraction spectrum is disclosed, wherein an organiccompound capable of forming a phthalocyanine ring and a titaniumcompound are made to react with each other at 130° C. for about 4 hoursin dialkylamino alcohol to which urea or ammonia is added (for example,refer to the following patent document 1).

Also, a method for producing an oxo-titanylphthalocyanine crystal isdisclosed in which o-phthalonitrile is made to react directly withtitanium tetrabutoxide without using a urea compound at 215° C. forabout 2 hours (for example, refer to the following patent documents 2and 3).

More specifically, disclosed is a method for producing anoxo-titanylphthalocyanine crystal having a peak in a predetermined rangein a CuKα characteristic X-ray diffraction spectrum and no temperaturevariation peak in a temperature range from 50 to 400° C. in differentialscanning calorimetric analysis.

However, in the case of the patent document 1, the addition proportionof the titanium compound to the organic compound capable of forming aphthalocyanine ring is small whereas the addition proportion of urea andthe like to the organic compound capable of forming a phthalocyaninering is excessive and also, reaction temperature is low. There istherefore the problem that produced Y-type oxo-titanylphthalocyaninecrystals tend to undergo crystal transition into β-type or α-typecrystals in a photoreceptive layer application liquid. For this reason,the photoreceptive layer application liquid is deteriorated in storagestability, with the result that there is the problem that nophotoreceptive layer having good electric properties can be stablyformed.

On the other hand, in the case of using the oxo-titanylphthalocyaninecrystals described in the patent documents 2 and 3, there is a problemconcerning low dispersibility in a photoreceptive layer though thecrystal transition in the photoreceptive layer application liquid can besuppressed to some extent. As a result, there are problems concerningreduced sensitivity and reduced charge retention rate inelectrophotographic photoreceptors using the oxo-titanylphthalocyaninecrystals as charge generating agents.

[Patent document 1] JP-A H08-176456 (examples) [Patent document 2] JP3463032 (claims) [Patent document 3] JP-A 2004-145284 (claims) SUMMARYOF THE INVENTION

In view of this situation, the inventors of the present invention havemade earnest studies concerning the above problems, and as a result,found that an oxo-titanylphthalocyanine crystal which is stable and issuperior in dispersibility in a photoreceptive layer can be obtained bywashing a wet cake, which is an intermediate product, with apredetermined alcohol in a process of producing an oxo-phthalocyaninecrystal having predetermined optical characteristics and thermalstability.

Specifically, it is an object of the present invention to provide anoxo-titanylphthalocyanine crystal which is stable, is superior indispersibility in a photoreceptive layer and efficiently contributes toimprovements in sensitivity and charge retention rate of anelectrophotographic photoreceptor when it is contained in theelectrophotographic photoreceptor as a charge generating agent, a methodfor producing the oxo-titanylphthalocyanine crystal, and anelectrophotographic photoreceptor.

According to an aspect of the present invention, there is provided anoxo-titanylphthalocyanine crystal having a maximum diffraction peak at aBragg angle (2θ±0.2°)=27.2° in the CuKα characteristic X-ray diffractionspectrum and one peak in a temperature range from 270 to 400° C. otherthan the peak derived from vaporization of adsorbed water indifferential scanning calorimetric analysis, theoxo-titanylphthalocyanine crystal being produced by a production methodincluding the following steps (a) to (d), whereby the aforementionedproblem can be solved:

(a) a step of dissolving a crude oxo-titanylphthalocyanine crystal in anacid to obtain an oxo-titanylphthalocyanine solution;

(b) a step of adding the oxo-titanylphthalocyanine solution dropwise ina poor solvent to obtain a wet cake;

(c) a step of washing the wet cake with an alcohol having 1 to 4 carbonatoms; and

(d) a step of stirring the washed wet cake under heating in a nonaqueoussolvent to obtain an oxo-titanylphthalocyanine crystal.

Crystal transition to an α-type crystal and β-type crystal can beefficiently suppressed even when the oxo-titanylphthalocyanine crystalis dipped for a term as long as 7 days or more, for example, insofar asit has predetermined optical characteristics and thermalcharacteristics.

The oxo-titanylphthalocyanine crystal can improve dispersibility in thephotoreceptive layer insofar as it is produced through the predeterminedprocess.

The effect of improving dispersibility is considered to be obtained bywashing the wet cake with a predetermined alcohol in the step (c),thereby reforming the surface characteristics of theoxo-titanylphthalocyanine crystal.

In any case, the oxo-titanylphthalocyanine crystal of the presentinvention is stable and is superior in dispersibility in thephotoreceptive layer, and therefore, efficiently contributes toimprovements in sensitivity and charge retention rate of anelectrophotographic photoreceptor when it is contained in theelectrophotographic photoreceptor as a charge generating agent.

The wet cake shows the condition that oxo-phthalocyanine is dispersed ina relatively small amount of, for example, water and has a block form.

Also, when constituting the oxo-titanylphthalocyanine crystal of theinvention, the production method preferably includes the followinginspection steps (e) to (g) after the step (d):

(e) a step of adding the oxo-titanylphthalocyanine crystal in an amountby weight of 1.25 parts based on 100 parts by weight of a mixed solventof methanol and N,N-dimethylformamide(methanol:N,N-dimethylformamide=1:1 (by weight ratio)) to prepare asuspension;

(f) a step of filtering the suspension with a filter to obtain afiltrate; and

(g) a step of confirming that the absorbance of the filtrate for lighthaving a wavelength of 400 nm is a value in a range from 0.01 to 0.08.

Such a constitution ensures that when the absorbance of the filtrate ismeasured, the dispersibility of the oxo-titanylphthalocyanine crystal inthe photoreceptive layer can be evaluated easily and quantitatively.

The reason why the absorbance for light having a wavelength of 400 nm ismeasured as an index of dispersibility is that a correlation among theabsorbance for the light having such a wavelength, the dispersibility ofthe oxo-titanylphthalocyanine crystal and the electric characteristicsof the electrophotographic photoreceptor caused by the dispersibilityhas been empirically found.

Also, such a correlation is considered to be created because thecondition of reformation of surface characteristics of theoxo-titanylphthalocyanine crystal is reflected on the absorbance for thelight having a wavelength of 400 nm.

Further, when the oxo-titanylphthalocyanine crystal of the invention isconstituted, the acid used in the step (a) is preferably at least onetype selected from the group consisting of concentrated sulfuric acid,trifluoroacetic acid and sulfonic acid.

With such a constitution, impurities can be decomposed efficiently bysuch an acid whereas the decomposition of the oxo-titanylphthalocyaninecompound can be suppressed with high efficiency.

Furthermore, when constituting the oxo-titanylphthalocyanine crystal ofthe invention, the poor solvent used in the step (b) is preferablywater.

With such a constitution, the surface area of the wet cake obtained canbe increased, which allows the dispersibility of theoxo-titanylphthalocyanine crystal in the photoreceptive layer to beimproved more efficiently in the subsequent washing step.

Moreover, when the oxo-titanylphthalocyanine crystal of the invention isconstituted, the alcohol having 1 to 4 carbon atoms which is used in thestep (c) is preferably at least one type selected from the groupconsisting of methanol, ethanol and 1-propanol.

Such a constitution makes it possible to even more efficiently improvethe dispersibility of the oxo-titanylphthalocyanine crystal in thephotoreceptive layer.

Also, when the oxo-titanylphthalocyanine crystal of the invention isconstituted, it is preferable that the wet cake is washed with analcohol having 1 to 4 carbon atoms and then, further washed with waterin the step (c).

Such a constitution effectively suppresses the crystal transition of theoxo-titanylphthalocyanine crystal more efficiently, so that a morestable oxo-titanylphthalocyanine crystal can be obtained.

Also, when the oxo-titanylphthalocyanine crystal of the invention isconstituted, the oxo-titanylphthalocyanine crystal preferably has amaximum diffraction peak at a Bragg angle (2θ±0.2°)=27.2° in the CuKαcharacteristic X-ray diffraction spectrum measured after the crystal isdipped in an organic solvent for 24 hours and no peak at 26.2°.

Such a constitution enables a further improvement in the stability ofthe oxo-titanylphthalocyanine crystal in the photoreceptive layerapplication liquid.

According to another aspect of the present invention, there is provideda method for producing an oxo-titanylphthalocyanine crystal, theoxo-titanylphthalocyanine crystal having a maximum diffraction peak at aBragg angle (2θ±0.2°)=27.2° in the CuKα characteristic X-ray diffractionspectrum and one peak in a temperature range from 270 to 400° C. otherthan the peak derived from vaporization of adsorbed water indifferential scanning calorimetric analysis, the method including thefollowing steps (a) to (d):

(a) a step of dissolving a crude oxo-titanylphthalocyanine crystal in anacid to obtain an oxo-titanylphthalocyanine solution;

(b) a step of adding the oxo-titanylphthalocyanine solution dropwise ina poor solvent to obtain a wet cake;

(c) a step of washing the wet cake with an alcohol having 1 to 4 carbonatoms; and

(d) a step of stirring the washed wet cake under heating in a nonaqueoussolvent to obtain an oxo-titanylphthalocyanine crystal.

Specifically, an oxo-titanylphthalocyanine crystal having predeterminedoptical characteristics and thermal characteristics is produced throughpredetermined steps, which results in the production of anoxo-titanylphthalocyanine crystal which is stable and is superior indispersibility in a photoreceptive layer, and therefore efficientlycontributes to improvements in sensitivity and charge retention rate ofan electrophotographic photoreceptor when it is contained in theelectrophotographic photoreceptor as a charge generating agent

Also, when executing the method for producing anoxo-titanylphthalocyanine crystal according to the invention, the methodpreferably includes the following inspection steps (e) to (g) after thestep (d):

(e) a step of adding the oxo-titanylphthalocyanine crystal in an amountby weight of 1.25 parts based on 100 parts by weight of a mixed solventof methanol and N,N-dimethylformamide(methanol:N,N-dimethylformamide=1:1 (by weight ratio)) to prepare asuspension;

(f) a step of filtering the suspension with a filter to obtain afiltrate; and

(g) a step of confirming that the absorbance of the filtrate for lighthaving a wavelength of 400 nm is a value in a range from 0.01 to 0.08.

Such a constitution ensures that when the absorbance of the filtrate ismeasured, the dispersibility of the oxo-titanylphthalocyanine crystal inthe photoreceptive layer can be evaluated easily and quantitatively.

Accordingly, an oxo-titanylphthalocyanine crystal which is stable and issuperior in dispersibility in the photoreceptive layer can be producedmore stably.

According to a still another aspect of the present invention, there isprovided an electrophotographic photoreceptor including a substrate anda photoreceptive layer containing a charge generating agent, a chargetransfer agent and a binding resin formed on the substrate, wherein thecharge generating agent is an oxo-titanylphthalocyanine having a maximumdiffraction peak at a Bragg angle (2θ±0.2°)=27.2° in the CuKαcharacteristic X-ray diffraction spectrum and one peak in a temperaturerange from 270 to 400° C. other than the peak derived from vaporizationof adsorbed water in differential scanning calorimetric analysis, theoxo-titanylphthalocyanine crystal being produced by the following steps(a) to (d):

(a) a step of dissolving a crude oxo-titanylphthalocyanine crystal in anacid to obtain an oxo-titanylphthalocyanine solution;

(b) a step of adding the oxo-titanylphthalocyanine solution dropwise ina poor solvent to obtain a wet cake;

(c) a step of washing the wet cake with an alcohol having 1 to 4 carbonatoms; and

(d) a step of stirring the washed wet cake under heating in a nonaqueoussolvent to obtain an oxo-titanylphthalocyanine crystal.

Specifically, a predetermined oxo-titanylphthalocyanine crystal which isstable and is superior in dispersibility in the photoreceptive layer iscontained as the charge generating agent, which enables anelectrophotographic photoreceptor having excellent sensitivity andcharge retention rate to be obtained.

Also, when the electrophotographic photoreceptor of the invention isconstituted, the following relationship (1) is preferably establishedamong the reflection absorbance (A/−) of the photoreceptive layer forlight having a wavelength of 700 nm, the film thickness (d/m) of thephotoreceptive layer and the concentration (C/wt %) of theoxo-titanylphthalocyanine crystal in the photoreceptive layer.

A·C ⁻¹ ·d ⁻¹>1.75×10⁻⁴  (1)

Such a constitution makes it possible to confirm with ease thedispersibility of the oxo-titanylphthalocyanine crystal in thephotoreceptive layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph for explaining the relationship between the absorbanceand the sensitivity;

FIG. 2 is a graph for explaining the relationship between the absorbanceand the charge retention rate;

FIG. 3 is a graph for explaining the relationship between thedispersibility and the sensitivity;

FIGS. 4A and 4B are views for explaining the configuration of amonolayer type electrophotographic photoreceptor according to thepresent invention;

FIGS. 5A and 5B are views for explaining a method for measuring thereflection absorbance of a photoreceptive layer;

FIGS. 6A and 6B are views for explaining the configuration of a laminatetype electrophotographic photoreceptor according to the presentinvention;

FIG. 7 is a CuKα characteristic X-ray diffraction spectrum of anoxo-titanylphthalocyanine crystal used in examples; and

FIG. 8 is a differential scanning analysis chart of anoxo-titanylphthalocyanine crystal used in examples.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

A first embodiment of the present invention relates to anoxo-titanylphthalocyanine crystal having a maximum diffraction peak at aBragg angle (2θ±0.2°)=27.2° in a CuKα characteristic X-ray diffractionspectrum and one peak in a temperature range from 270 to 400° C. otherthan the peak derived from vaporization of adsorbed water indifferential scanning calorimetric analysis, theoxo-titanylphthalocyanine crystal being produced by a production methodincluding the following steps (a) to (d):

(a) a step of dissolving a crude oxo-titanylphthalocyanine crystal in anacid to obtain an oxo-titanylphthalocyanine solution;

(b) a step of adding the oxo-titanylphthalocyanine solution dropwise ina poor solvent to obtain a wet cake;

(c) a step of washing the wet cake with an alcohol having 1 to 4 carbonatoms; and

(d) a step of stirring the washed wet cake under heating in a nonaqueoussolvent to obtain an oxo-titanylphthalocyanine crystal.

The oxo-titanylphthalocyanine crystal will be explained in more detail.The steps (a) to (d) will be explained in the subsequent secondembodiment, and in this first embodiment, the characteristics, etc. ofthe oxo-titanylphthalocyanine crystal itself will be explained.

1. Oxo-Titanylphthalocyanine Compound

As an oxo-titanylphthalocyanine compound constituting theoxo-titanylphthalocyanine crystal of the invention, compoundsrepresented by the following formula (1) are preferable.

This is because an oxo-titanylphthalocyanine compound having such astructure not only enables further improvement in stability of theoxo-titanylphthalocyanine crystal but also enables such anoxo-titanylphthalocyanine crystal to be produced stably.

Also, particularly, the oxo-titanylphthalocyanine crystal preferably hasa structure represented by the following formula (2). Among thesecompounds, unsubstituted oxo-titanylphthalocyanine compounds representedby the following formula (3) are particularly preferable.

This is because the use of an oxo-titanylphthalocyanine compound havingsuch a structure makes it possible to more easily produce anoxo-titanylphthalocyanine crystal having more stable qualities:

(In the general formula (1), X¹, X², X³ and X⁴, which may be the same ordifferent substituents, each represents a hydrogen atom, a halogen atom,an alkyl group, an alkoxy group, a cyano group or a nitro group, andrepeat units a, b, c and d, which may be the same or different, eachdenote an integer from 1 to 4.)

(In the general formula (2), X represents a hydrogen atom, a halogenatom, an alkyl group, an alkoxy group, a cyano group or a nitro groupand a repeat unit e denotes an integer from 1 to 4.)

2. Oxo-Titanylphthalocyanine Crystal (1) Optical Characteristics

The oxo-titanylphthalocyanine crystal of the present invention ischaracterized by such optical characteristics that it has a maximumdiffraction peak at a Bragg angle (2θ±0.2°)=27.2° in the CuKαcharacteristic X-ray diffraction spectrum (first opticalcharacteristics).

It is preferable that the oxo-titanylphthalocyanine crystal of theinvention has no peak at 26.2° in the CuKα characteristic X-raydiffraction spectrum (second optical characteristics).

It is also preferable that the oxo-titanylphthalocyanine crystal of theinvention has no peak at a Bragg angle (2θ±0.2°)=7.2° in the CuKαcharacteristic X-ray diffraction spectrum (third opticalcharacteristics).

This is because if an oxo-titanylphthalocyanine crystal which is notprovided with the first optical characteristics is used, there is atendency that the stability of crystals in an organic solvent and chargegenerating ability are deteriorated more significantly than in the caseof using an oxo-titanylphthalocyanine crystal provided with the firstoptical characteristics. Conversely speaking, this is because if anoxo-titanylphthalocyanine crystal is provided with the first opticalcharacteristics, more preferably, the second and third characteristics,the stability of a crystal in an organic solvent and charge generatingability can be improved.

It is preferable that the oxo-titanylphthalocyanine crystal has amaximum diffraction peak at least at a Bragg angle (2θ±0.2°)=27.2° andno peak at a Bragg angle (2θ±0.2°)=26.2° in the CuKα characteristicX-ray diffraction spectrum measured after dipped for 24 hours in anorganic solvent.

This reason is that when the oxo-titanylphthalocyanine crystal has suchcharacteristics, the stability of the crystal with time anddispersibility of the crystal in the photoreceptive layer applicationliquid can be more improved.

Specifically, this is because it can be confirmed that even in the caseof dipping the oxo-titanylphthalocyanine crystal for 24 hours in anorganic solvent such as tetrahydrofuran in actual, the crystal type isnot transited to an α or β-type but retains a predetermined crystaltype, and it is therefore possible to control crystal transition in anorganic solvent.

Note that the dipping experiment in an organic solvent for evaluation,which is a criterion for the evaluation of the storage stability of theoxo-titanylphthalocyanine crystal is preferably made in the samecondition that is used to actually store, for example, a photoreceptivelayer application liquid used to manufacture the electrophotographicphotoreceptor (hereinafter referred to simply as photoreceptorapplication liquid). It is therefore preferable to evaluate the storagestability of the oxo-titanylphthalocyanine crystal in a closed systemunder the condition of a temperature of 23±1° C. and a relative humidityof 50 to 60% RH, for example.

Also, the organic solvent used when evaluating the storage stability ofthe oxo-titanylphthalocyanine crystal is preferably at least one typeselected from the group consisting of tetrahydrofuran, dichloromethane,toluene, 1,4-dioxane and 1-methoxy-2-propanol.

This is because when such an organic solvent is used as the organicsolvent in the photoreceptive layer application liquid, the stability ofthe oxo-titanylphthalocyanine crystal can be estimated more exactly, andalso, the solvent is highly compatible with, for example, theoxo-titanylphthalocyanine crystal, charge transfer agent and bindingresin. Accordingly, a photoreceptor that allows, for example, theoxo-titanylphthalocyanine crystal and charge transfer agent to exhibittheir characteristics can be formed, and an electrophotographicphotoreceptor superior in electric characteristics and imagecharacteristics can be produced resultantly.

(2) Thermal Characteristics

The oxo-titanylphthalocyanine crystal according to the invention is alsocharacterized by such thermal characteristics that it has one peak in atemperature range from 270 to 400° C. other than the peak derived fromvaporization of adsorbed water in differential scanning calorimetricanalysis.

This is because crystal transition of the crystal structure to an α-typecrystal and β-type crystal can be efficiently suppressed even when theoxo-titanylphthalocyanine crystal is dipped in an organic solvent for along term insofar as it has the aforementioned optical characteristicsand thermal characteristics. Therefore, a photoreceptive layerapplication liquid superior in storage stability can be obtained byusing such an oxo-titanylphthalocyanine crystal, with the result that anelectrophotographic photoreceptor superior in electric characteristicsand image characteristics can be stable produced.

The aforementioned one peak which is a peak other than the peak derivedfrom the vaporization of adsorbed water and appears in a temperaturerange from 270 to 400° C. appears more preferably in a temperature rangefrom 290 to 400° C., and still more preferably in a temperature rangefrom 300 to 400° C.

A specific method for measuring the Bragg angle in the CuKαcharacteristic X-ray diffraction spectrum and a specific method ofdifferential scanning calorimetric analysis will be explained in detailin Examples described later.

Second Embodiment

A second embodiment of the present invention relates to a method forproducing an oxo-titanylphthalocyanine crystal having a maximumdiffraction peak at a Bragg angle (2θ±0.2°)=27.2° in a CuKαcharacteristic X-ray diffraction spectrum and one peak in a temperaturerange from 270 to 400° C. other than the peak derived from vaporizationof adsorbed water in differential scanning calorimetric analysis, themethod including the following steps (a) to (d):

(a) a step of dissolving a crude oxo-titanylphthalocyanine crystal in anacid to obtain an oxo-titanylphthalocyanine solution;

(b) a step of adding the oxo-titanylphthalocyanine solution dropwise ina poor solvent to obtain a wet cake;

(c) a step of washing the wet cake with an alcohol having 1 to 4 carbonatoms; and

(d) a step of stirring the washed wet cake under heating in a nonaqueoussolvent to obtain an oxo-titanylphthalocyanine crystal.

The content which has already been explained in the first embodimentwill be properly omitted to explain the method for producing anoxo-titanylphthalocyanine compound according to the second embodiment.

1. Production of oxo-titanylphthalocyanine Compound

In the method for producing an oxo-titanylphthalocyanine compound,production materials of this molecule, specifically, o-phthalonitrile orits derivative, or 1,3-diiminoisoindoline or its derivative, titaniumalkoxide or titanium tetrachloride are preferably made to rear with eachother in the presence of a urea compound to produce anoxo-titanylphthalocyanine compound.

Specifically, the method is preferably performed according to thefollowing reaction formula (1) or (2). In the reaction formula (1) or(2), titanium tetrabutoxide represented by the formula (5) is used astitanium alkoxide, by way of example.

(1) Reaction Formula

It is therefore preferable that o-phthalonitrile represented by theformula (4) is made to react with titanium tetrabutoxide as the titaniumalkoxide represented by the formula (5) as shown in the reaction formula(1) or 1,3-diiminoisoindoline represented by the formula (6) is made toreact with titanium tetrabutoxide as the titanium alkoxide representedby the formula (5) as shown in the reaction formula (2), to produce anoxo-titanylphthalocyanine compound represented by the formula (3).

In this case, titanium tetrachloride may be used in place of thetitanium alkoxide such as titanium tetrabutoxide represented by theformula (5).

(2) Addition Quantity

The addition quantity of the titanium alkoxide such as titaniumtetrabutoxide represented by the formula (5) or titanium tetrachlorideis preferably a value ranging from 0.40 to 0.53 mol based on 1 mol ofo-phthalonitrile represented by the formula (4) or its derivative or of1,3-diiminoisoindoline represented by the formula (6) or its derivative.

This is because when the titanium alkoxide such as titaniumtetrabutoxide represented by the formula (5) or titanium tetrachlorideis added in an amount exceeding ¼ mol equivalents to o-phthalonitrilerepresented by the formula (4) or its derivative or to1,3-diiminoisoindoline represented by the formula (6) or its derivative,an interaction with a urea compound which will be explained later iseffected in an efficient manner. Such an interaction will be describedin detail in the paragraph as to the urea compound.

Therefore, the addition quantity of the titanium alkoxide such astitanium tetrabutoxide represented by the formula (5) or titaniumtetrachloride is more preferably a value ranging from 0.42 to 0.50 mol,and still more preferably a value ranging from 0.45 to 0.47 mol based on1 mol of o-phthalonitrile represented by the formula (4) or1,3-diiminoisoindoline represented by the formula (6), etc.

(3) Urea Compound

Also, the reaction represented by the above reaction formulae (1) and(2) is preferably made in the presence of a urea compound. This isbecause when an oxo-titanylphthalocyanine compound produced in thepresence of a urea compound is used, an interaction between the ureacompound and titanium alkoxide or titanium tetrachloride is effected tothereby obtain a specific oxo-titanylphthalocyanine crystal efficiently.

Specifically, the interaction means an action of the materials concernedon promotion of the reaction represented by the reaction formulae (1)and (2) wherein ammonia produced by the reaction of the urea compoundwith the titanium alkoxide or titanium tetrachloride further forms acomplex with titanium alkoxide or titanium chloride and the complex morepromotes the reaction. Such a promotion action makes it possible toefficiently produce an oxo-titanylphthalocyanine crystal resistant tocrystal transition even in an organic solvent by reacting the rawmaterials.

(3)-1 Type

The urea compound to be used in the reaction formulae (1) and (2) ispreferably at least one type selected from the group consisting of urea,thiourea, O-methylisourea sulfate, O-methylisourea carbonate andO-methylisourea hydrochloride.

This reason is that when such a urea compound is used as the ureacompound shown in the reaction formulae (1) and (2), ammonia generatedin the reaction process forms a complex in combination with titaniumalkoxide or titanium tetrachloride more efficiently and the complexfurther promotes the reaction represented by the reaction formulae (1)and (2).

Specifically, ammonia generated by the reaction between titaniumalkoxide or titanium tetrachloride as a raw material and a urea compoundfurther efficiently forms a complex compound in combination withtitanium alkoxide, etc. Therefore, the complex compound further promotesthe reaction represented by the reaction formulae (1) and (2).

It has been clarified that such a complex compound tends to be producedpeculiarly when the reaction is made at a temperature as high as 180° C.or more. For this reason, it is more effective to perform the reactionin a nitrogen-containing compound, for example, quinoline (boilingpoint: 237.1° C.) or isoquinoline (boiling point: 242.5° C.) or amixture of them (by weight ratio: 10:90 to 90:10).

Among the aforementioned urea compounds, urea is more preferably usedbecause ammonia which is a reaction accelerator and the complex compoundgenerated by the aid of ammonia are generated more easily.

(3)-2 Addition Quantity

The addition quantity of the urea compound to be used in the reactionrepresented by the reaction formulae (1) and (2) is preferably a valuein a range from 0.1 to 0.95 mol based on 1 mol of o-phthalonitrile orits derivative or 1,3-diiminoisoindoline or its derivative.

This is because the action of the urea compound described above can beexhibited when the addition quantity of the urea compound is made tofall in the above range.

Therefore, the addition quantity of the urea compound is more preferablya value in a range from 0.2 to 0.8 mol, and still more preferably avalue in a range from 0.3 to 0.7 mol based on 1 mol of o-phthalonitrileor its derivative or 1,3-diiminoisoindoline or its derivative.

(4) Solvent

Examples of the solvent to be used in the reaction represented by thereaction formulae (1) and (2) include a single compound or a combinationof two or more compounds selected from the group consisting of:hydrocarbon type solvents such as xylene, naphthalene,methylnaphthalene, tetralin and nitrobenzene; hydrocarbon halide typesolvents such as dichlorobenzene, trichlorobenzene, dibromobenzene andchloronaphthalene; alcoholic solvents such as hexanol, octanol, decanol,benzyl alcohol, ethylene glycol and diethylene glycol; ketone typesolvents such as cyclohexanone, acetophenone, 1-methyl-2-pyrrolidone and1,3-dimethyl-2-imidazolidinone; amide type solvents such as formamideand acetamide; and nitrogen-containing solvents such as picoline,quinoline and isoquinoline.

Particularly, nitrogen-containing compounds having a boiling point of180° C. or more, such as quinoline and isoquinoline, are preferablesolvents because ammonia produced by the reaction of the titaniumalkoxide or titanium tetrachloride as the raw material with the ureacompound tends to form a complex with titanium alkoxide or the like moreefficiently.

(5) Reaction Temperature

The temperature of the reaction represented by the reaction formulae (1)and (2) is preferably designed to be a temperature as high as 150° C. ormore. This is because if the reaction temperature is less than 150° C.,particularly 135° C. or less, titanium alkoxide or titaniumtetrachloride as the raw material scarcely reacts with the ureacompound, which makes it difficult to form a complex compound. Thisgives difficulty in producing the situation where the complex compoundfurther promotes the reaction represented by the reaction formulae (1)and (2). It is therefore difficult to produce anoxo-titanylphthalocyanine crystal which is resistant to crystaltransition even in an organic solvent in an efficient mannerresultantly.

Accordingly, the temperature of the reaction represented by the reactionformulae (1) and (2) is more preferably a value in a range from 180 to250° C., and still more preferably a value in a range from 200 to 240°C.

(6) Reaction Time

The reaction time in the reaction represented by the reaction formulae(1) and (2), though depending on the reaction temperature, is preferablyin a range from 0.5 to 10 hours. This is because if the reaction time isless than 0.5 hours, the titanium alkoxide or titanium tetrachloride asthe raw material scarcely reacts with the urea compound, thereby givingdifficulty in forming a complex compound. This makes it difficult forthe complex compound to further promote the reaction represented by thereaction formulae (1) and (2), with the result of difficulty inproducing an oxo-titanylphthalocyanine crystal which is resistant tocrystal transition even in an organic solvent in an efficient manner. Ifthe reaction time exceeds 10 hours, on the other hand, this may beeconomically disadvantageous or the produced complex compound may bedecreased.

Therefore, the reaction time in the reaction represented by the reactionformulae (1) and (2) is more preferably a value in a range from 0.6 to3.5 hours, and still more preferably a value in a range from 0.8 to 3hours.

2. Method for Producing an oxo-titanylphthalocyanine Crystal (1)Pre-Acid Treatment Step

Then, as a pre-stage prior to acid treatment for theoxo-titanylphthalocyanine compound produced in the above step or othersteps, a pre-acid treatment step is preferably performed in which theoxo-titanylphthalocyanine compound is added in an aqueous organicsolvent, the mixture is stirred under heating for a fixed time and thenthe solution is allowed to stand at a temperature lower than thestirring temperature for a fixed time, followed by being subjected tostabilizing treatment.

Examples of the aqueous organic solvent used in the pre-acid treatmentinclude one type or two or more types of alcohols such as methanol,ethanol and isopropanol, N,N-dimethylformamide, N,N-dimethylacetamide,propionic acid, acetic acid, N-methylpyrrolidone and ethylene glycol. Anonaqueous organic solvent may be added to an aqueous organic solvent ifits amount is small.

Though no particular limitation is imposed on the condition of thestirring treatment in the pre-acid treatment step, it is preferable toperform stirring treatment in the condition of a fixed temperature ofabout 70 to 200° C. for about 1 to 3 hours.

Moreover, though there is no particular limitation to the condition ofthe stabilizing treatment after the stirring treatment, the solution ispreferably allowed to stand in the condition of a fixed temperaturerange of about 10 to 50° C. and particularly about 23±1° C. for 5 to 15hours to stabilize. The pre-acid treatment is executed in this manner toobtain a crude oxo-titanylphthalocyanine crystal.

(2) Acid Treatment Step

Then, the acid treatment step is characterized in that the crudeoxo-titanylphthalocyanine crystal is dissolved in an acid to obtain anoxo-titanylphthalocyanine solution.

This is because the crude oxo-titanylphthalocyanine crystal is dissolvedin an acid to enable to sufficiently decompose impurities derived fromsubstances left unremoved when the oxo-titanylphthalocyanine compound isproduced.

The acid to be used is preferably at least one type selected from thegroup consisting of concentrated sulfuric acid, trifluoroacetic acid andsulfonic acid.

This reason is that such an acid can decompose the above-describedimpurities more efficiently whereas it can efficiently suppressdecomposition of the oxo-titanylphthalocyanine compound.

Also, the reason is that after such an acid treatment, componentsderived from these acids can be easily removed by washing as will beexplained later.

The acid treatment step is preferably executed usually at 0 to 10° C.for 0.5 to 3.0 hours, though these conditions differ depending on theacid to be used.

(3) Dropwise Addition Step

Then, the oxo-titanylphthalocyanine solution obtained in the acidtreatment step is added dropwise to a poor solvent to obtain a wet cake.

This is because washing effect in the subsequent washing step can beproduced efficiently by adding the oxo-titanylphthalocyanine solutiondropwise to a poor solvent.

Specifically, this is because the wet cake of the precipitatedoxo-titanylphthalocyanine compound is put into an amorphous state havinga large surface area by the dropwise addition, and therefore, thewashing effect in the subsequent washing step can be producedefficiently.

Also, the poor solvent to be used is preferably water.

This reason is that water can precipitate an oxo-titanylphthalocyaninecompound more easily from the viewpoint of polarity and temperaturecontrol.

Consequently, the surface area of the wet cake of the precipitatedoxo-titanylphthalocyanine compound is increased to perform the washingstep more efficiently.

Other usable poor solvents may include methanol, ethanol or a mixedsolvent of methanol and water or a mixed solvent of ethanol and water.

Note that the temperature of the poor solvent is usually designed to bein a range from 0 to 20° C., though it differs depending on the type ofthe poor solvent to be used.

(4) Washing Step

Then, the wet cake of the oxo-titanylphthalocyanine compound obtained inthe dropwise addition step is washed with an alcohol having 1 to 4carbon atoms.

This is because washing the wet cake with an alcohol having 1 to 4carbon atoms enables efficient improvement in the dispersibility of theoxo-titanylphthalocyanine crystal obtained in the subsequent crystaltype transformation step in the photoreceptive layer. The effect ofimproving the dispersibility is considered to be obtained by reformingthe surface properties of the oxo-titanylphthalocyanine crystal.

In any case, the washing with a predetermined alcohol makes it possibleto stably obtain an oxo-titanylphthalocyanine crystal which is superiorin dispersibility in a photoreceptive layer and contributes toimprovements in sensitivity and charge retention rate of anelectrophotographic photoreceptor when the oxo-titanylphthalocyaninecrystal is added to the electrophotographic photoreceptor as a chargegenerating agent.

The alcohol having 1 to 4 carbon atoms is preferably at least one typeselected from the group consisting of methanol, ethanol and 1-propanol.

This reason is that any of these alcohols can improve the dispersibilityof the oxo-titanylphthalocyanine crystal in the photoreceptive layermore efficiently.

It is also preferable that the wet cake is washed with an alcohol having1 to 4 carbon atoms, and then further washed with water.

This is because when the wet cake is further washed with water afterwashed with a predetermined alcohol, the crystal transition of theoxo-titanylphthalocyanine crystal can be suppressed to obtain a morestable oxo-titanylphthalocyanine crystal.

The washing operations with an alcohol having 1 to 4 carbon atoms andwater are preferably repeated plural times, respectively.

To mention the washing method in more detail, for example, about 10 g ofthe wet cake may be dipped in about of 500 ml of a predetermined alcoholor water and suspended by stirring or the like to perform washing.

Also, the temperature of the predetermined alcohol or water used in thewashing is designed to be preferably in a range from 0 to 50° C., andmore preferably in a range from 10 to 40° C. The washing time isdesigned to be preferably in a range from 5 minutes to 10 hours, andmore preferably in a range from 0.5 to 8 hours.

(5) Crystal Type Transformation Step

Then, the wet cake obtained after the washing step is stirred underheating in an nonaqueous solvent to obtain an oxo-titanylphthalocyaninecrystal.

This reason is that if the wet cake of the oxo-titanylphthalocyaninecrystal is stirred under heating in a nonaqueous solvent, the crystaltype can be transformed into a predetermined crystal type having theoptical characteristics and thermal characteristics explained in thefirst embodiment.

In the above stirring under heating, the wet cake is preferablydispersed in the nonaqueous solvent in the presence of water and stirredat 30 to 70° C. for 5 to 40 hours.

Examples of the nonaqueous solvent include halogen type solvents such aschlorobenzene and dichloromethane.

(6) Inspection Step

The following inspection steps (e) to (g) are preferably involved afterthe aforementioned crystal type transformation step:

(e) a step of adding the oxo-titanylphthalocyanine crystal in an amountby weight of 1.25 parts based on 100 parts by weight of a mixed solventof methanol and N,N-dimethylformamide(methanol:N,N-dimethylformamide=1:1 (by weight ratio)) to prepare asuspension;

(f) a step of filtering the suspension with a filter to obtain afiltrate; and

(g) a step of confirming that the absorbance of the filtrate for lighthaving a wavelength of 400 nm is a value in a range from 0.01 to 0.08.

This reason is that if the absorbance of a predetermined filtrateobtained through the above steps is measured, the dispersibility of theoxo-titanylphthalocyanine crystal in the photoreceptive layer can beevaluated easily and quantitatively, and it is therefore possible toproduce more stably an oxo-titanylphthalocyanine crystal which is stableand is superior in dispersibility in the photoreceptive layer.

Specifically, this is because when the absorbance of the filtrate forlight having a wavelength of 400 nm is less than 0.01, a problem as tothe formation of an oxo-titanylphthalocyanine crystal itself may arise,whereas when the absorbance of the filtrate for light having awavelength of 400 nm exceeds 0.08, the dispersibility of theoxo-titanylphthalocyanine crystal may tend to decrease, which is a causeof a reduction in sensitivity and charge retention rate in anelectrophotographic photoreceptor.

Therefore, the absorbance of the filtrate for light having a wavelengthof 400 nm is more preferably a value in a range from 0.012 to 0.07, andstill more preferably a value in a range from 0.012 to 0.05.

The reason why the absorbance for light having a wavelength of 400 nm ismeasured as an index of dispersibility is that a correlation among theabsorbance for the light having such a wavelength, the dispersibility ofthe oxo-titanylphthalocyanine crystal and the electric characteristicsof the electrophotographic photoreceptor caused by the dispersibilityhas been empirically found.

Also, such a correlation is considered to be created because thecondition of reformation of surface characteristics of theoxo-titanylphthalocyanine crystal is reflected on the absorbance for thelight having a wavelength of 400 nm.

A method for measuring the absorbance of a predetermined filtrate willbe explained in Examples explained later.

As to the condition under which the suspension is obtained in the step(e), a suspension obtained by stirring in the stirring condition of atemperature of 23±3° C. and a rotational speed of 100 rpm for 1 hour isused.

As to the amount of the mixed solvent used to suspend theoxo-titanylphthalocyanine crystal, methanol and N-dimethylamide aremixed in a total amount of 8 g (4 g each).

The amount of the oxo-titanylphthalocyanine crystal to be suspended isdesigned to be 0.1 g.

Also, as the filter used to filter the suspension in the step (f), a0.1-μm filter which is a PTFE type is used.

Moreover, the absorbing layer (filtrate) when the absorbance is measuredin the step (g) is designed to have a thickness of 10 mm (cell length).

Then, 1.25 parts by weight of a predetermined oxo-titanylphthalocyaninecrystal is added to 100 parts by weight of a mixed solvent of methanoland N,N-dimethylformamide (methanol:N,N-dimethylformamide=1:1 (by weightratio)) to prepare a suspension, and then, the suspension is filteredwith a filter to obtain a filtrate. With reference to FIG. 1,description will be given to the relation between the absorbance of thefiltrate for light having a wavelength of 400 nm and the sensitivity ofan electrophotographic photoreceptor containing theoxo-titanylphthalocyanine crystal as a charge generating agent.

Specifically, FIG. 1 shows a characteristic curve, in which the abscissais the absorbance (−) of the above predetermined filtrate for lighthaving a wavelength of 400 nm while the ordinate is the absolute value(V) of the sensitivity of the electrophotographic photoreceptor. Forexample, the configuration of the electrophotographic photoreceptor anda method for measuring the sensitivity will be described in Examples.

As is understood from the characteristic curve, the absolute value (V)of the sensitivity increases with an increase in the value of theabsorbance (−) of the predetermined filtrate. Note that a smallerabsolute value (V) of the sensitivity means that the electrophotographicphotoreceptor has more excellent sensitivity characteristics.

To explain more specifically, it is understood that as the value of theabsorbance (−) of the predetermined filtrate increases 0 to 0.08, theabsolute value (V) of the sensitivity sharply increases from about 40 Vwhile the absolute value takes on a value of about 60 V or less.

It is also understood that when the value of the absorbance (−) of thepredetermined filtrate exceeds 0.08 on the other hand, the absolutevalue (V) of the sensitivity takes on a value as higher as about 60 V ormore, though an increase in the absolute value (V) of the sensitivity ismoderate.

Therefore, it is understood that in order to limit the absolute value(V) of the sensitivity to about 60 V or less to obtain excellentsensitivity characteristics, it is effective to set the value of theabsorbance (−) of the predetermined filtrate to a value of 0.08 or less.

1.25 parts by weight of a predetermined oxo-titanylphthalocyaninecrystal is added to 100 parts by weight of a mixed solvent of methanoland N,N-dimethylformamide (methanol:N,N-dimethylformamide=1:1 (by weightratio)) to prepare a suspension and then, the suspension is filteredwith a filter to obtain a filtrate. With reference to FIG. 2,description will be given to the relation between the absorbance of thefiltrate for light having a wavelength of 400 nm and the chargeretention rate (%) of an electrophotographic photoreceptor containingthe oxo-titanylphthalocyanine crystal as a charge generating agent.

Specifically, FIG. 2 shows a characteristic curve, in which the abscissais the absorbance (−) of the above predetermined filtrate for lighthaving a wavelength of 400 nm while the ordinate is the charge retentionrate (%) of the electrophotographic photoreceptor. For example, theconfiguration of the electrophotographic photoreceptor and a method formeasuring the charge retention rate will be described in Examples.

As is understood from the characteristic curve, the value of the chargeretention rate (%) decreases with an increase in the value of theabsorbance (−) of the predetermined filtrate. Note that a larger chargeretention rate (%) means that an electrostatic latent image formed onthe surface of the electrophotographic photoreceptor can be retained fora longer time and the electrophotographic photoreceptor is superior inelectric characteristics.

To explain more specifically, it is understood that as the value of theabsorbance (−) of the predetermined filtrate increases 0 to 0.08, thevalue of the charge retention rate (%) slightly sharply decreases fromabout 100% while the charge retention rate (%) takes on a value of about97.5% or more.

It is also understood that when the value of the absorbance (−) of thepredetermined filtrate exceeds 0.08 on the other hand, the chargeretention rate (%) takes on a value as low as about 97.5% or less,though a reduction in the value of the charge retention rate (%) ismoderate.

Therefore, it is understood that in order to keep the value of thecharge retention rate (%) at a level of about 97.5% or more to obtainsuperior electric characteristics, it is effective to set the value ofthe absorbance (−) of the predetermined filtrate to a value of 0.08 orless.

Next, the relationship between the dispersibility of theoxo-titanylphthalocyanine crystal in the photoreceptive layer and thesensitivity of the electrophotographic photoreceptor will be explainedwith reference to FIG. 3.

Here, as the index of dispersibility, a parameter (A·C⁻¹·d⁻¹) (unit:1/(wt %·m), the same as follows) is used which is constituted of thereflection absorbance (A/−) for light having a wavelength of 700 nm inthe photoreceptive layer containing the oxo-titanylphthalocyaninecrystal, the film thickness (d/m) of the photoreceptive layer and theconcentration (C/wt %) of the oxo-titanylphthalocyanine crystal in thephotoreceptive layer. The parameter and a method for measuring thereflection absorbance of the photoreceptive layer will be explainedlater. Fundamentally, the parameter is used for the evaluation of thedispersibility of the oxo-titanylphthalocyanine crystal in thephotoreceptive layer according to the Lambert-Beer's law.

Specifically, in FIG. 3, the abscissa is the value of (A·C⁻¹·d⁻¹), theleft ordinate is the absolute value (V) of the sensitivity of theelectrophotographic photoreceptor in relation to a characteristic curveA and the right ordinate is the dispersibility (relative evaluation) ofthe oxo-titanylphthalocyanine crystal in the photoreceptive layer inrelation to a characteristic curve B.

Also, the relative evaluation of the dispersibility of theoxo-titanylphthalocyanine crystal in the photoreceptive layer is basedon the results of observation using a microscope.

As is understood from the characteristic curve B, the dispersibility(relative evaluation) of the oxo-titanylphthalocyanine crystal is moreimproved with an increase in the value of (A·C⁻¹·d⁻¹).

In other words, a larger value of (A·C⁻¹·d⁻¹) shows that thedispersibility of the oxo-titanylphthalocyanine crystal in thephotoreceptive layer is higher.

Thus, it can be said that the dispersibility of theoxo-titanylphthalocyanine crystal can be clearly evaluated by the valueof (A·C⁻¹·d⁻¹).

As is understood from the characteristic curve A, the absolute value ofthe sensitivity is reduced with an increase in the value of (A·C⁻¹·d⁻¹).

Therefore, when the results of the characteristic curves A and B areevaluated overall, it can be said that the sensitivity of theelectrophotographic photoreceptor is more improved with an increase inthe dispersibility of the oxo-titanylphthalocyanine crystal.

As a consequence, it can be said that the sensitivity of theelectrophotographic photoreceptor is improved more efficiently by usingthe oxo-titanylphthalocyanine crystal superior in dispersibilityaccording to the present invention.

It has been separately confirmed that the charge retention rate of thephotographic photoreceptor is also clearly related with thedispersibility of the oxo-titanylphthalocyanine crystal similarly to thecase of the sensitivity.

Note that when the electrophotographic photoreceptor is a laminate type,the dispersibility of the oxo-titanylphthalocyanine crystal may beevaluated by using its charge generating layer as the subject.

Third Embodiment

A third embodiment of the present invention relates to anelectrophotographic photoreceptor including a substrate and aphotoreceptive layer containing a charge generating agent, a chargetransfer agent and a binding resin, the photoreceptive layer beingformed on the substrate, wherein the charge generating agent is anoxo-titanylphthalocyanine crystal having a maximum diffraction peak at aBragg angle (2θ±0.2°)=27.2° in a CuKα characteristic X-ray diffractionspectrum and one peak in a temperature range from 270 to 400° C. otherthan the peak derived from vaporization of adsorbed water indifferential scanning calorimetric analysis, theoxo-titanylphthalocyanine crystal being produced by a production methodincluding the following steps (a) to (d):

(a) a step of dissolving a crude oxo-titanylphthalocyanine crystal in anacid to obtain an oxo-titanylphthalocyanine solution;

(b) a step of adding the oxo-titanylphthalocyanine solution dropwise ina poor solvent to obtain a wet cake;

(c) a step of washing the wet cake with an alcohol having 1 to 4 carbonatoms; and

(d) a step of stirring the washed wet cake under heating in a nonaqueoussolvent to obtain an oxo-titanylphthalocyanine crystal.

The contents which have been already explained in the first and secondembodiments are appropriately omitted, and the electrophotographicphotoreceptor of the third embodiment will be explained by primarilytaking a monolayer type photographic photoreceptor as an example.

1. Basic Configuration

As shown in FIG. 4A, the basic configuration of an electrophotographicphotoreceptor 10 according to the invention preferably includes asubstrate 12 and a single photoreceptive layer 14 formed on thesubstrate 12, the photoreceptive layer containing a specific chargegenerating agent, a charge transfer agent and a binding resin.

This reason is that the monolayer type electrophotographic photoreceptor10 can be applied to both positive and negative charge types and alsoenables a simple layer structure, which makes it possible to suppresscoating film defects and to improve productivity when the photoreceptivelayer is formed.

This reason is also that optical characteristics can be improved becausethe number of interfaces between layers is small.

As is illustrated in FIG. 4B, a monolayer type photoreceptor 10′ havingan intermediate layer 16 formed between the photoreceptive layer 14 andthe substrate 12 may be adopted.

2. Substrate

Various materials having conductivity may be used as the substrate 12illustrated in FIG. 4. Examples of these materials include metals suchas iron, aluminum, copper, tin, platinum, silver, vanadium, molybdenum,chromium, cadmium, titanium, nickel, palladium, indium, stainless steeland brass; plastic materials coated with the above metal by depositionor lamination; and glasses coated with, for example, alumite, aluminumiodide, tin oxide or indium oxide.

The shape of the substrate may be any form including a sheet-form anddrum-form in accordance with the structure of an image forming apparatusto be used. It is only required for the substrate itself or its surfaceto have conductivity. In addition, the substrate is preferably onehaving sufficient mechanical strength upon use. In the case of adrum-form, the diameter of the substrate is designed to be in a rangefrom 10 to 60 mm, and more preferably from 10 to 35 mm in view ofdeveloping a small-sized device.

In order to prevent the generation of interference fringes, the surfaceof the support substrate may be subjected to surface roughing treatmentusing a method such as etching, anodic oxidation, wet blasting method,sand blasting method, rough abrasion and centerless cutting.

When the substrate is subjected to, for example, anodic oxidation, thesubstrate may have nonconductive or semiconductive characteristics. Evenin such a case, it may be used as the substrate insofar as it producespredetermined effects.

3. Intermediate Layer

As shown in FIG. 4B, an intermediate layer 16 containing a predeterminedbinding resin may be formed on the substrate 12.

This is because the intermediate layer improves the adhesion between thesubstrate and the photoreceptive layer and also, the addition of thepredetermined binding resin micropowder to the intermediate layerensures that incident light is scattered to thereby suppress not onlythe generation of interference fringes but also the injection of chargesinto the photoreceptive layer during unexposed time, that is the causeof fogging and black spots. Any material may be used as the micropowderwithout any particular limitation insofar as it has light-scatteringability and dispersibility. Examples of the micropowder include whitepigments such as titanium oxide, zinc oxide, zinc flower, zinc sulfide,zinc white and lithopone; inorganic pigments as extenders such asalumina, calcium carbonate and barium sulfate; fluororesin particles;benzoguanamine resin particles; and styrene resin particles.

The film thickness of the intermediate layer is preferably a value in arange from 0.1 to 50 μm. This is because if the intermediate layer istoo thick, residual potential may tend to arise on the surface of thephotoreceptor, which is a cause of deteriorated electriccharacteristics, whereas if the intermediate layer is too thin, thesurface irregularities of the substrate can be insufficiently flattened,thereby failing to obtain the adhesion between the substrate and thephotoreceptive layer.

For this reason, the thickness of the intermediate layer is preferably avalue in a range from 0.1 to 50 μm, and more preferably a value in arange from 0.5 to 30 μm.

4. Photoreceptive Layer (1) Binding Resin

No particular limitation is imposed on the type of the binding resin tobe used in the photographic photoreceptor of the invention. Usableexamples of the binding resin include, in addition to a polycarbonateresin, thermoplastic resins such as a polyester resin, polyarylateresin, styrene-butadiene copolymer, styrene-acrylonitrile copolymer,styrene-maleic acid copolymer, acryl copolymer, styrene-acrylic acidcopolymer, polyethylene, ethylene-vinyl acetate copolymer, polyethylenechloride, polyvinyl chloride, polypropylene, ionomer, vinylchloride-vinyl acetate copolymer, alkyd resin, polyamide, polyurethane,polysulfone, diallyl phthalate resin, ketone resin, polyvinylbutyralresin and polyether resin; crosslinking thermosetting resins such as asilicone resin, epoxy resin, phenol resin, urea resin and melamineresin; and photocurable resins such as epoxyacrylate andurethaneacrylate.

(2) Charge Generating Agent

The charge generating agent to be used in the invention is anoxo-titanylphthalocyanine crystal having a maximum diffraction peak at aBragg angle (2θ±0.2°)=27.2° in a CuKα characteristic X-ray diffractionspectrum and one peak in a temperature range from 270 to 400° C. otherthan the peak derived from vaporization of adsorbed water indifferential scanning calorimetric analysis, theoxo-titanylphthalocyanine crystal being obtained by a production methodincluding the following steps (a) to (d):

(a) a step of dissolving a crude oxo-titanylphthalocyanine crystal in anacid to obtain an oxo-titanylphthalocyanine solution;

(b) a step of adding the oxo-titanylphthalocyanine solution dropwise ina poor solvent to obtain a wet cake;

(c) a step of washing the wet cake with an alcohol having 1 to 4 carbonatoms; and

(d) A step of stirring the washed wet cake under heating in a nonaqueoussolvent to obtain an oxo-titanylphthalocyanine.

This is because such an oxo-titanylphthalocyanine crystal has crystalstability and is also superior in dispersibility in the photoreceptivelayer, which enables to obtain an electrophotographic photoreceptorhaving excellent sensitivity and charge retention rate.

The details of the oxo-titanylphthalocyanine crystal as the chargegenerating agent are overlapped on the descriptions in the first andsecond embodiments, and are therefore omitted.

The addition quantity of the oxo-titanylphthalocyanine crystal as thecharge generating agent is preferably designed to be in a range from 0.1to 50 parts by weight based on 100 parts by weight of the binding resinwhich will be explained later.

This reason is that if the addition quantity of the charge generatingagent is made to be in the above range, the charge generating agent cangenerate charges efficiently when the electrophotographic photoreceptoris exposed to light. In other words, the reason is that if the additionquantity of the charge generating agent is less than 0.1 part by weightbased on 100 parts by weight of the binding resin, the amount of thecharge generating agent may be not enough to form an electrostaticlatent image on the photoreceptor, whereas if the addition quantity ofthe charge generating agent exceeds 50 parts by weight based on 100parts by weight of the binding resin, it may be difficult to dispersethe charge generating agent uniformly in the photoreceptive layerapplication liquid.

For this reason, the addition quantity of the charge generating agent ismore preferably a value in a range from 0.5 to 30 parts by weight basedon 100 parts by weight of the binding resin.

(3) Hole Transfer Agent

Also, no particular limitation is imposed on the hole transfer agent tobe used in the invention, and conventionally known various hole transfercompounds may be all used. Preferably usable hole transfer compoundsinclude a benzidine type compound, a phenylenediamine type compound, anaphthylenediamine type compound, a phenanethrylenediamine typecompound, an oxadiazole type compound (for example,2,5-di(4-methylaminophenyl)-1,3,4-oxadiazole), a styryl type compound(for example, 9-(4-diethylaminostyryl)anthracene), a carbazole typecompound (for example, poly-N-vinylcarbazole), an organic polysilanecompound, a pyrazoline type compound (for example,1-phenyl-3-(p-dimethylaminophenyl)pyrazoline), a hydrazone typecompound, a triphenylamine type compound, an indole type compound, anoxazole type compound, an isooxazole type compound, a thiazole typecompound, a thiadiazole type compound, an imidazole type compound, apyrazole type compound, a triazole type compound, a butadiene typecompound, a pyrene-hydrazone type compound, an acrolein type compound, acarbazole-hydrazone type compound, a quinoline-hydrazone type compound,a stilbene type compound, a stilbene-hydrazone type compound and adiphenylenediamine type compound. These compounds are used independentlyor may be used in combinations of two or more.

Also, the addition quantity of the hole transfer agent is preferablydesigned to be in a range from 1 to 120 parts by weight of 100 parts byweight of the binding resin.

This is because if the addition quantity of the hole transfer agent isless than 1 part by weight, the hole transfer ability of thephotoreceptive layer may be remarkably deteriorated to thereby give anadverse influence on image characteristics, whereas if the additionquantity of the hole transfer agent exceeds 120 parts by weight, thisgives rise to the problem that the dispersibility of the hole transferagent is deteriorated and the hole transfer agent is easilycrystallized.

Therefore, the addition quantity of the hole transfer agent is morepreferably a value in a range from 5 to 100 parts by weight, and stillmore preferably a value in a range from 10 to 90 parts by weight basedon 100 parts by weight of the binding resin.

(4) Electron Transfer Agent

No particular limitation is imposed on the electron transfer agent to beused in the invention. Preferably usable electron transfer agentsinclude a benzoquinone type compound, a naphthoquinone type compound, ananthraquinone type compound, a diphenoquinone type compound, adinaphthoquinone type compound, a naphthalenetetracarboxylic aciddiimide type compound, a fluorenone type compound, a malononitrile typecompound, a thiopyran type compound, a trinitrothioxanthone typecompound, a dinitroanthracene type compound, a dinitroacridine typecompound, a nitroanthraquinone type compound, and a dinitroanthraquinonetype compound. These compounds are used independently or may be used incombinations of two or more.

The addition quantity of the electron transfer agent is preferablydesigned to be 1 to 120 parts by weight based on 100 parts by weight ofthe binding resin.

This is because if the addition quantity of the electron transfer agentis less than 1 part by weight, the electron transfer ability of thephotoreceptive layer is remarkably deteriorated to thereby give anadverse influence on image characteristics, whereas if the additionquantity of the electron transfer exceeds 120 parts by weight, thisgives rise to the problem that the dispersibility of the electrontransfer agent is deteriorated and the electron transfer agent is easilycrystallized.

Therefore, the addition quantity of the electron transfer agent is morepreferably a value in a range from 5 to 100 parts by weight, and stillmore preferably a value in a range from 10 to 90 parts by weight basedon 100 parts by weight of the binding resin.

(5) Thickness

The film thickness of the photoreceptive layer is preferably designed tobe in a range from 5.0 to 100 μm.

This reason is that if the thickness of the photoreceptive layer is lessthan 5.0 μm, the mechanical strength required for theelectrophotographic photoreceptor may be insufficient, whereas if thethickness of the photoreceptive layer exceeds 100 μm, the photoreceptivelayer may tend to peel from the substrate and it may be difficult toform the photoreceptive layer uniformly. For this reason, the thicknessof the photoreceptive layer is more preferably a value in a range from10 to 80 μm, and still more preferably a value in a range from 20 to 40μm.

(6) Relational Expression (1)

Also, the following relational expression (1) is preferably establishedbetween the reflection absorbance (A/−) of the photoreceptive layer forlight having a wavelength of 700 nm, the film thickness (d/m) of thephotoreceptive layer and the concentration (C/wt %) of theoxo-titanylphthalocyanine crystal in the photoreceptive layer.

A·C ⁻¹ ·d ⁻¹>1.75×10⁻⁴  (1)

This reason is that in the case of a photoreceptive layer satisfying therelational expression (1), the dispersibility of theoxo-titanylphthalocyanine crystal in the photoreceptive layer is easilyconfirmed.

Specific reason is as follows: as explained with reference to FIG. 3 inthe second embodiment, there is a clear correlation between the value of(A·C⁻¹·d⁻¹) (1/(wt %·m)) which is the left side of the relationalexpression (1) and the dispersibility of the oxo-titanylphthalocyaninecrystal in the photoreceptive layer. Therefore, the dispersibility ofthe oxo-titanylphthalocyanine crystal in the photoreceptive layer andthe electric characteristics of the electrophotographic photoreceptorwhich are dependent on the dispersibility can be easily confirmed byobserving whether the value (A·C⁻¹·d⁻¹) is in the predetermined range ornot.

Here, the left side (A·C⁻¹·d⁻¹) of the relational expression (1) isregarded as a parameter expressing the dispersibility of theoxo-titanylphthalocyanine crystal in the photoreceptive layer accordingto the Lambert-Beer's law.

Specifically, this reason is that when the film thickness (d/m) of thephotoreceptive layer and the concentration (C/wt %) of theoxo-titanylphthalocyanine crystal in the photoreceptive layer are fixed,incident light is scarcely absorbed and reflection absorbance (A) forlight having a wavelength of 700 nm tends to be small if thedispersibility of the oxo-titanylphthalocyanine crystal in thephotoreceptive layer is insufficient, whereas if the dispersibility ofthe oxo-titanylphthalocyanine crystal is insufficient, incident light iseasily absorbed and reflection absorbance (A) of the photoreceptivelayer for light having a wavelength of 700 nm is large.

Therefore, it is understood from this reason that the dispersibility ofthe oxo-titanylphthalocyanine crystal in the photoreceptive layer can beevaluated from the value of the left side (A·C⁻¹·d⁻¹) of the relationalexpression (1).

When the electrophotographic photoreceptor is a laminate type, itscharge generating layer is used as the subject to evaluate thedispersibility of the oxo-titanylphthalocyanine crystal.

With reference to FIG. 3, description will be given to the relationbetween the value of A·C⁻¹·d⁻¹ (unit: 1/(wt %·m), the same as follows)which is the let side of the relational expression (1)) and thesensitivity of the electrophotographic photoreceptor.

Specifically, in FIG. 3, the abscissa is the value of (A·C⁻¹·d⁻¹) andthe ordinate (left axis) is the absolute value (V) of the sensitivity toshow a characteristic curve A.

As is understood from the characteristic curve A, as the value of(A·C⁻¹·d⁻¹) is closer to 0, the absolute value (V) of the sensitivity islarger, whereas as the value of (A·C⁻¹·d⁻¹) is larger, the absolutevalue (V) of the sensitivity is smaller. To mention in more detail, itis understood that as the value of (A·C⁻¹·d⁻¹) is increased, theabsolute value (V) of the sensitivity sharply drops when the value of(A·C⁻¹·d⁻¹) is in a range from 0 to 1.75×10⁴. It is also understood thatas the value of (A·C⁻¹·d⁻¹) is increased, the absolute value (V) of thesensitivity gradually drops and takes a value of 60 V or less when thevalue of (A·C⁻¹·d⁻¹) is in a range above 1.75×10⁴.

The value of (A·C⁻¹·d⁻¹) is designed to be more preferably 1.9×10⁴ ormore and still more preferably 2.0×10⁴ or more.

The reflection absorbance (A/−) of the photoreceptive layer for lighthaving a wavelength of 700 nm may be measured, for example, in thefollowing manner.

First, the reflection absorbance (A₁) of a support substrate on which aphotoreceptive layer (standard thickness: 2.5×10⁻⁵ m) is laminated, forlight having a wavelength of 700 nm is measured by a color differencemeter (trade name: Color Difference Meter CM1000, manufactured byMinolta Camera Co., Ltd.). Next, the reflection absorbance (A₂) of asupport substrate on which no photoreceptive layer is laminated, forlight having a wavelength of 700 nm is measured in the same manner asabove.

More detailed explanations will be furnished with reference to FIGS. 5Aand 5B, in which FIG. 5A shows the condition of the support substrate 12on which the photoreceptive layer 14 is laminated and FIG. 5B shows thecondition of only the support substrate 12 on which no photoreceptivelayer 14 is laminated. I₀ in FIGS. 5A and 5B denotes the intensity oflight (incident light) applied to each support substrate, and I₁ and I₂denote the intensities of the reflections of the lights incident to therespective support substrates. In order to eliminate the influence ofthe support substrate to obtain the reflection absorbance of thephotoreceptive layer, it is only necessary to subtract the reflectionabsorbance A₂ of the support substrate from the reflection absorbance A₁in which the reflection absorbances of the photoreceptive layer andsupport substrate are intermingled.

Then, the reflection absorbance (A) of an intermediate layer may becalculated from the following numerical formula (1) based on the values(A₁, A₂) of the obtained reflection absorbances.

The reflection absorbance (A₁) in FIG. 5A is calculated from thefollowing numerical formula (2), and, similarly, the reflectionabsorbance (A₂) in FIG. 5B is calculated from the following numericalformula (3).

A=A ₁ −A ₂  (1)

A ₁=−Log I ₁ /I ₀  (2)

A ₂=−Log I ₂ /I ₀  (3)

5. Production Method

Though no particular limitation is imposed on the method for producing amonolayer type photographic photoreceptor, the method may be performedaccording to the following procedures. First, a specific chargegenerating agent, charge transfer agent, binding resin and otheradditives are added in a solvent to prepare an application liquid. Theobtained application liquid is applied to a conductive substrate(aluminum preliminary pipe) by, for example, a dip coat method, a spraycoating method, a beads coating method, a blade coating method and aroller coating method.

Thereafter, the coating layer is dried by hot air at 100° C. for 30minutes to obtain a monolayer type photographic photoreceptor thatincludes a photoreceptive layer having a fixed film thickness.

Various organic solvents may be used as the solvent used to prepare thedispersion solution. Examples of the solvent include alcohols such asmethanol, ethanol, isopropanol and butanol; aliphatic hydrocarbons suchas n-hexane, octane and cyclohexane; aromatic hydrocarbons such asbenzene, toluene and xylene; halogenated hydrocarbons such asdichloromethane, dichloroethane, chloroform, carbon tetrachloride andchlorobenzene; ethers such as dimethyl ether, diethyl ether,tetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycoldimethyl ether, 1,3-dioxolan and 1,4-dioxane; ketones such as acetone,methyl ethyl ketone and cyclohexanone; esters such as ethyl acetate andmethyl acetate; dimethylformaldehyde, dimethylformamide anddimethylsulfoxide. These solvents may be used either singly or incombinations of two or more. At this time, a surfactant, a levelingagent and the like may be compounded in order to improve thedispersibility of the charge generating agent and the smoothness of thesurface of the photoreceptive layer.

Also, it is preferable to form an intermediate layer on the substratebefore the photoreceptive layer is formed.

In the formation of this intermediate layer, the binding resin and,according to the need, additives (organic micropowder or inorganicmicropowder) are mixed and dispersed using a known method using a rollmill, a ball mill, an attritor, a paint shaker, an ultrasonic dispersingmachine or the like to prepare an application liquid. The applicationliquid is applied to the substrate by known measures, for example, ablade method, a dipping method or a spraying method, followed by heattreatment to form an intermediate layer.

A small amount of various additives (organic micropowder or inorganicmicropowder) may be added within a range free of problems concerningprecipitation in the production process, with the intention of, forexample, scattering light to thereby prevent the generation ofinterference fringes.

Next, the obtained application liquid may be applied to, for example,the surface of a support substrate (aluminum preliminary pipe) by acoating method such as a dip coat method, a spray coating method, abeads coating method, a blade coating method and a roller coatingmethod.

The subsequent step of drying the application liquid on the substrate isperformed at a temperature from 20 to 200° C. for 5 minutes to 2 hours.

Various organic solvents may be used as a solvent used to prepare theapplication liquid. Examples of the solvent include alcohols such asmethanol, ethanol, isopropanol and butanol; aliphatic hydrocarbons suchas n-hexane, octane and cyclohexane; aromatic hydrocarbons such asbenzene, toluene and xylene; halogenated hydrocarbons such asdichloromethane, dichloroethane, chloroform, carbon tetrachloride andchlorobenzene; ketones such as acetone, methyl ethyl ketone andcyclohexanone; esters such as ethyl acetate and methyl acetate;dimethylformaldehyde, dimethylformamide and dimethylsulfoxide. Thesesolvents may be used either singly or in combinations of two or more.

6. Laminate Type Electrophotographic Photoreceptor

When constituting the electrophotographic photoreceptor of the presentinvention, as shown in FIG. 6, the photoreceptive layer is alsopreferably a laminate type photoreceptive layer 20 including a chargegenerating layer 24 containing a specific charge generating agent and acharge transfer layer 22 containing a charge transfer agent and abinding resin.

The laminate type electrophotographic photoreceptor 20 may bemanufactured by forming a charge generating layer 24 containing aspecific charge generating agent on a substrate 12 by means of vapordeposition or coating, and then applying an application liquidcontaining a charge transfer agent and a binding resin on the chargegenerating layer 24, followed by drying the application liquid to form acharge transfer layer 22.

Contrary to the above structure, the charge transfer layer 22 is formedon the substrate 12 and the charge generating layer 24 may be formed onthe charge transfer layer 22 as shown in FIG. 6B. Because the chargegenerating layer 24 has a very lower thickness than the charge transferlayer 22, it is preferable to form the charge transfer layer 22 on thecharge generating layer 24 to protect the charge generating layer 24 asshown in FIG. 6A.

Also, an intermediate layer 25 is preferably formed on the substrate inthe same manner as in the case of the monolayer type photoreceptor.

Also, the charge generating layer forming application liquid and thecharge transfer layer forming application liquid may be prepared, forexample, by dispersing/mixing predetermined components such as aspecific charge generating agent, a charge transfer agent and a bindingresin together with a dispersion medium by using a roll mill, a ballmill, an attritor, a paint shaker, an ultrasonic dispersing machine orthe like.

Though no particular limitation is imposed on the thickness of thephotoreceptive layer (charge generating layer and charge transfer layer)in the laminate type photoreceptive layer 20, the thickness of thecharge generating layer is preferably 0.01 to 5 μm and more preferably0.1 to 3 μm and the thickness of the charge transfer layer is preferably2 to 100 μm and more preferably 5 to 50 μm.

EXAMPLES

The present invention will be explained in detail by way of Examples.

Example 1 1. Production of oxo-titanylphthalocyanine Compound

A flask in which the atmosphere was substituted with argon was chargedwith 22 g (0.17 mol) of o-phthalonitrile, 25 g (0.073 mol) of titaniumtetrabutoxide, 300 g of quinoline and 2.28 g (0.038 mol) of urea, andthe mixture was heated to 150° C. with stirring.

Then, the reaction system was heated to 215° C. while removing the vaporgenerated from the reaction system out of the system and then thereaction was further continued for 2 hours with stirring while keepingthis temperature.

Then, after the reaction was finished, the reaction mixture was cooled.When the mixture was cooled to 150° C., the reaction mixture was takeout of the flask and subjected to filtration using a glass filter. Theobtained solid was washed with N,N-dimethylformamide and methanol inthis order, followed by vacuum drying to obtain 24 g of a bluish violetsolid.

2. Production of oxo-titanylphthalocyanine Crystal (1) PretreatmentPrior to Pigmentation Treatment

12 g of the bluish violet solid obtained in the above production of theoxo-titanylphthalocyanine compound was added in 100 ml ofN,N-dimethylformamide, and the mixture was heated to 130° C. for 2 hoursto perform stirring treatment.

Then, the heating was stopped after two hours passed, and the mixturewas cooled. When the mixture was cooled to 23±1° C., the stirring wasalso stopped, and in this state, the solution was allowed to stand for12 hours to perform stabilizing treatment. Then, after stabilized, thesupernatant was separated by filtration using a glass filter, and theobtained solid was washed with methanol and then dried under vacuum toobtain 11.8 g of a crude crystal of an oxo-titanylphthalocyaninecompound.

(2) Pigmentation Treatment

10 g of the crude crystal of the oxo-titanylphthalocyanine compoundobtained in the above pretreatment prior to pigmentation treatment wasadded and dissolved in 100 g of 97% concentrated sulfuric acid. Thisacid treatment was performed at 5° C. for one hour.

Next, the solution was added dropwise to 5 l of ice-cooled purifiedwater at a rate of 10 ml/min, and the mixture was stirred at about 15±3°C. for 30 minutes and then allowed to stand for 30 minutes. Then, thesolution was subjected to filtration using a glass filter to obtain awet cake.

Subsequently, the obtained wet cake was suspended in 500 ml of methanolto wash it, and after washing, methanol was removed by filtration usinga glass filter. Such washing was repeated four times. Then, the obtainedwet cake was suspended in 500 ml of 20° C. purified water to wash it,and after washing, water was removed by filtration using a glass filter.

5 g of the washed wet cake was added to 0.75 g of water and 100 g ofchlorobenzene, and the mixture was stirred under heating at 50° C. for24 hours.

Then, the crystal obtained by subjecting the supernatant to filtrationusing a glass filter was washed with 100 ml of methanol on a funnel andthen dried under vacuum at 50° C. for 5 hours, to obtain 4.5 g of acrystal of unsubstituted oxo-titanylphthalocyanine (blue powder)represented by the formula (3).

3. Evaluation of oxo-titanylphthalocyanine Crystal (1) Measurement ofCuKα Characteristic X-Ray Diffraction Spectrum

0.3 g of the obtained oxo-titanylphthalocyanine crystal was dispersed in5 g of tetrahydrofuran, which was then stored in a sealed system kept ata temperature of 23±1° C. under a relative humidity of 50 to 60% for 24hours in a sealed system, and then tetrahydrofuran was removed. Themixture was charged in a sample holder in a X-ray diffraction device(trade name: RINT1100, manufactured by Rigaku Corporation to measure.The obtained spectrum chart is shown in Table 7. The spectrum chart hasthe characteristics that there is the maximum peak at a Bragg angle(2θ±0.2°)=27.2° and no peak at 26.2°. It has been confirmed from thisfact that the obtained oxo-titanylphthalocyanine crystal has a stableand predetermined crystal type. This is because the peak at a Braggangle (2θ±0.2°)=27.2° is specific to the above predetermined crystaltype and the peak at 26.2° is specific to a β-type crystal.

The measuring condition was as follows.

X-ray tube globe: CuTube voltage: 40 kVTube current: 30 mAStart angle: 3.0°Stop angle: 40.0°Scanning speed: 10°/min

(2) Differential Scanning Calorimetric Analysis

The obtained oxo-titanylphthalocyanine crystal was subjected todifferential scanning calorimetric analysis using a differentialscanning calorimeter (trade name: TAS-200 model, DSC8230D, manufacturedby Rigaku Corporation). The obtained differential scanning analysischart is shown in FIG. 8. In this chart, other than a peak derived fromvaporization of adsorbed water, one peak was confirmed at 296° C.

The measuring condition was as follows.

Sample pan: made of aluminumTemperature rise rate: 20° C./min

(3) Measurement of Absorbance

0.1 g (1.25 parts by weight) of the obtained oxo-titanylphthalocyaninecrystal was added to 8 g (100 parts by weight) of a mixed solventconstituted of methanol and N,N-dimethylformamide(methanol:N,N-dimethylformamide=1:1 (by weight ratio). The mixture wasstirred at a rotational speed of 100 rpm for one hour while keeping atemperature of 23° C. to obtain a suspension. Then, the obtainedsuspension was subjected to filtration using a PTFE type 0.1-μm membranefilter (manufactured by Advantest Corporation) to obtain a filtrate.Subsequently, the obtained filtrate was stored in a cell having a lengthof 10 mm to measure absorbance of the filtrate for light having awavelength of 400 nm by using an absorptiometer (trade name:Spectrophotometer U3000, manufactured by HITACHI, Ltd.) The obtainedresults are shown in Table 1.

4. Production of an Electrophotographic Photoreceptor (1) Formation ofIntermediate Layer

250 parts by weight of titanium oxide (trade name: MT-02, manufacturedby Tayca Corporation, surface treated with alumina, silica and silicone,number average primary particle diameter: 10 nm), 100 parts by weight ofa quaternary copolymer polyamide resin (trade name: CM8000, manufacturedby Toray Industries, Inc.) and a solvent consisting of 1000 parts byweight of methanol and 250 parts by weight of n-butanol were mixed anddispersed for 5 hours. The dispersion was further subjected tofiltration using a 5-μ filter to prepare an intermediate layerapplication liquid.

Then, an aluminum substrate (support substrate) of 30 mm in diameter and238.5 mm in length was dipped in the obtained intermediate layerapplication liquid at a rate of 5 mm/sec in such a manner that one endof the substrate faced upward, to apply the application liquid.Thereafter, curing treatment was performed at 130° C. for 30 minutes toform an intermediate layer having a film thickness of 2 μm.

(2) Formation of Charge Generating Layer

Then, 250 parts by weight of the oxo-titanylphthalocyanine crystalproduced in the above manner as a charge generating agent, 100 parts byweight of a polyvinylbutyral resin as a binding resin and 8000 parts byweight of tetrahydrofuran as a dispersing medium were mixed anddispersed for 48 hours by using a beads mill to obtain a chargegenerating layer application liquid. The obtained application liquid wassubjected to filtration using a 3-μ filter, and then the filtrateapplication liquid was applied to the intermediate layer by a dip coatmethod, followed by drying at 80° C. for 5 minutes to form a chargegenerating layer of 0.2 μm in film thickness.

(3) Formation of Charge Transfer Layer

Next, stored in an ultrasonic dispersing machine are 55 parts by weightof a compound (HTM-1) represented by the following formula (7) as a holetransfer agent, 5 parts by weight of methaterphenyl as an additive, 60parts by weight of a polycarbonate resin having a viscosity averagemolecular weight of 20,000 and 40 parts by weight of a polycarbonateresin having a viscosity average molecular weight of 50,000 as bindingresins and 310 parts by weight of tetrahydrofuran and 310 parts byweight of toluene as solvents. The mixture was subjected to dispersingtreatment performed for 10 minutes, to obtain a charge transfer layerapplication liquid.

The obtained charge transfer layer application liquid was applied to thesurface of the charge generating layer in the same manner as in the caseof the charge generating layer application liquid and dried at 120° C.for 30 minutes to form a charge transfer layer of 20 μm in filmthickness, thereby manufacturing a laminate type electrophotographicphotoreceptor.

5. Evaluation (1) Measurement of Sensitivity

The sensitivity of the obtained photographic photoreceptor was measured.

Specifically, using a drum sensitivity tester (manufactured by GENTECInc.), the electrophotographic photoreceptor was charged such that thesurface potential of the photoreceptor became −850 V. Then, the surfaceof the electrophotographic photoreceptor was exposed to monochromaticlight (half value width: 20 nm, light intensity: 1.0 μJ/cm²) having awavelength of 780 nm which light was extracted from white light by usinga bandpass filter (irradiation time: 50 msec). Subsequently, thepotential of the surface of the photoreceptor was measured as thesensitivity 350 msec after the surface of the photoreceptor was exposedto light. The results are shown in Table 1. The measured potential takeson a negative value and therefore, the absolute value of the measuredpotential is described in Table 1.

(2) Measurement of Charge Retention Rate

The charge retention rate of the obtained photographic photoreceptor wasmeasured.

Specifically, using a drum sensitivity tester (manufactured by GENTECInc.), the electrophotographic photoreceptor was charged such that thesurface potential of the photoreceptor became −850 V. Then, thepotential of the surface of the photoreceptor was measured one secondafter the surface of the photoreceptor was charged, to measure a chargeretention rate (%). The results are shown in Table 1.

Example 2

In Example 2, an oxo-titanylphthalocyanine crystal was produced andalso, an electrophotographic photoreceptor was produced to evaluate inthe same manner as in Example 1 except that in the pigmentationtreatment when the oxo-titanylphthalocyanine crystal was produced, thewet cake was washed three times with methanol and then twice with water.The obtained results are shown in Table 1. The results of the CuKαcharacteristic X-ray diffraction spectrum and differential scanningcalorimetric analysis of the obtained oxo-titanylphthalocyanine crystalwere the same as those of Example 1.

Example 3

In Example 3, an oxo-titanylphthalocyanine crystal was produced andalso, an electrophotographic photoreceptor was produced to evaluate inthe same manner as in Example 1 except that in the pigmentationtreatment when the oxo-titanylphthalocyanine crystal was produced, thewet cake was washed twice with methanol and then three times with water.The obtained results are shown in Table 1. The results of the CuKαcharacteristic X-ray diffraction spectrum and differential scanningcalorimetric analysis of the obtained oxo-titanylphthalocyanine crystalwere the same as those of Example 1.

Example 4

In Example 4, an oxo-titanylphthalocyanine crystal was produced andalso, an electrophotographic photoreceptor was produced to evaluate inthe same manner as in Example 1 except that in the pigmentationtreatment when the oxo-titanylphthalocyanine crystal was produced, thewet cake was washed once with methanol and then four times with water.The obtained results are shown in Table 1. The results of the CuKαcharacteristic X-ray diffraction spectrum and differential scanningcalorimetric analysis of the obtained oxo-titanylphthalocyanine crystalwere the same as those of Example 1.

Comparative Example 1

In Comparative Example 1, an oxo-titanylphthalocyanine crystal wasproduced and also, an electrophotographic photoreceptor was produced toevaluate in the same manner as in Example 1 except that in thepigmentation treatment when the oxo-titanylphthalocyanine crystal wasproduced, the wet cake was not washed with methanol but washed fivetimes with 60° C. water. The obtained results are shown in Table 1. Theresults of the CuKα characteristic X-ray diffraction spectrum anddifferential scanning calorimetric analysis of the obtainedoxo-titanylphthalocyanine crystal were the same as those of Example 1.

Comparative Example 2

In Comparative Example 2, an oxo-titanylphthalocyanine crystal wasproduced and also, an electrophotographic photoreceptor was produced toevaluate in the same manner as in Example 1 except that in thepigmentation treatment when the oxo-titanylphthalocyanine crystal wasproduced, the wet cake was not washed with methanol but washed threetimes with 60° C. water. The obtained results are shown in Table 1. Theresults of the CuKα characteristic X-ray diffraction spectrum anddifferential scanning calorimetric analysis of the obtainedoxo-titanylphthalocyanine crystal were the same as those of Example 1.

Comparative Example 3

In Comparative Example 3, an oxo-titanylphthalocyanine crystal wasproduced and also, an electrophotographic photoreceptor was produced toevaluate in the same manner as in Example 1 except that in thepigmentation treatment when the oxo-titanylphthalocyanine crystal wasproduced, the wet cake was not washed with methanol but washed threetimes with 20° C. water. The obtained results are shown in Table 1. Theresults of the CuKα characteristic X-ray diffraction spectrum anddifferential scanning calorimetric analysis of the obtainedoxo-titanylphthalocyanine crystal were the same as those of Example 1.

TABLE 1 Absolute value of Charge retention Absorbance sensitivity rate λ= 400 nm (V) (%) Example 1 0.012 47 99.4 Example 2 0.038 56 98.4 Example3 0.052 55 98.6 Example 4 0.062 55 99.2 Comparative 0.095 63 96.9Example 1 Comparative 0.110 68 95.6 Example 2 Comparative 0.201 65 95.7Example 3

According to the present invention, an oxo-titanylphthalocyanine crystalwhich is stable and has excellent dispersibility can be obtained in sucha manner that a wet cake which is an intermediate product is washed witha predetermined alcohol in the course of production of theoxo-titanylphthalocyanine crystal having predetermined opticalcharacteristics and thermal characteristics.

According to the method for producing oxo-titanylphthalocyanine crystalof the present invention, it is possible to stably produce anoxo-titanylphthalocyanine crystal which is stable and has excellentdispersibility in the photoreceptive layer.

Therefore, the electrophotographic photoreceptor using theoxo-titanylphthalocyanine crystal as the charge generating agent isexpected to contribute to improvement in electric properties and tostabilization of qualities in various image forming devices such ascopying machines and printers.

1. An oxo-titanylphthalocyanine crystal having a maximum diffractionpeak at a Bragg angle (2θ±0.2°)=27.2° in a CuKα characteristic X-raydiffraction spectrum and one peak in a temperature range from 270 to400° C. other than the peak derived from vaporization of adsorbed waterin differential scanning calorimetric analysis, theoxo-titanylphthalocyanine crystal being produced by a production methodcomprising the following steps (a) to (d): (a) a step of dissolving acrude oxo-titanylphthalocyanine crystal in an acid to obtain anoxo-titanylphthalocyanine solution; (b) a step of adding theoxo-titanylphthalocyanine solution dropwise in a poor solvent to obtaina wet cake; (c) a step of washing the wet cake with an alcohol having 1to 4 carbon atoms; and (d) a step of stirring the washed wet cake underheating in a nonaqueous solvent to obtain an oxo-titanylphthalocyaninecrystal.
 2. The oxo-titanylphthalocyanine crystal according to claim 1,wherein the production method comprises the following inspection steps(e) to (g) after the step (d): (e) a step of adding theoxo-titanylphthalocyanine crystal in an amount by weight of 1.25 partsbased on 100 parts by weight of a mixed solvent of methanol andN,N-dimethylformamide (methanol:N,N-dimethylformamide=1:1 (by weightratio)) to prepare a suspension; (f) a step of filtering the suspensionwith a filter to obtain a filtrate; and (g) a step of confirming thatthe absorbance of the filtrate for light having a wavelength of 400 nmis in a range from 0.01 to 0.08.
 3. The oxo-titanylphthalocyaninecrystal according to claim 1, wherein the acid used in the step (a) isat least one type selected from the group consisting of concentratedsulfuric acid, trifluoroacetic acid and sulfonic acid.
 4. Theoxo-titanylphthalocyanine crystal according to claim 1, wherein the poorsolvent used in the step (b) is water.
 5. The oxo-titanylphthalocyaninecrystal according to claim 1, wherein the alcohol having 1 to 4 carbonatoms which is used in the step (c) is at least one type selected fromthe group consisting of methanol, ethanol and 1-propanol.
 6. Theoxo-titanylphthalocyanine crystal according to claim 1, wherein the wetcake was washed with the alcohol having 1 to 4 carbon atoms, and furtherwashed with water in the step (c).
 7. The oxo-titanylphthalocyaninecrystal according to claim 1, wherein the oxo-titanylphthalocyaninecrystal has a maximum diffraction peak at a Bragg angle (2θ±0.2°)=27.2°in the CuKα characteristic X-ray diffraction spectrum measured after itis dipped in an organic solvent for 24 hours and no peak at 26.2°.
 8. Amethod for producing an oxo-titanylphthalocyanine crystal, theoxo-titanylphthalocyanine crystal having a maximum diffraction peak at aBragg angle (2θ±0.2°)=27.2° in a CuKα characteristic X-ray diffractionspectrum and one peak in a temperature range from 270 to 400° C. otherthan the peak derived from vaporization of adsorbed water indifferential scanning calorimetric analysis, the method comprising thefollowing steps (a) to (d): (a) a step of dissolving a crudeoxo-titanylphthalocyanine crystal in an acid to obtain anoxo-titanylphthalocyanine solution; (b) a step of adding theoxo-titanylphthalocyanine solution dropwise in a poor solvent to obtaina wet cake; (c) a step of washing the wet cake with an alcohol having 1to 4 carbon atoms; and (d) a step of stirring the washed wet cake underheating in a nonaqueous solvent to obtain an oxo-titanylphthalocyaninecrystal.
 9. The method for producing an oxo-titanylphthalocyaninecrystal according to claim 8, the method comprising the followinginspection steps (e) to (g) after the step (d): (e) a step of adding theoxo-titanylphthalocyanine crystal in an amount by weight of 1.25 partsbased on 100 parts by weight of a mixed solvent of methanol andN,N-dimethylformamide (methanol:N,N-dimethylformamide=1:1 (by weightratio)) to prepare a suspension; (f) a step of filtering the suspensionwith a filter to obtain a filtrate; and (g) a step of confirming thatthe absorbance of the filtrate for light having a wavelength of 400 nmis in a range from 0.01 to 0.08.
 10. An electrophotographicphotoreceptor comprising a substrate and a photoreceptive layercontaining a charge generating agent, a charge transfer agent and abinding resin, the photoreceptive layer being formed on the substrate,wherein the charge generating agent is an oxo-titanylphthalocyaninecrystal having a maximum diffraction peak at a Bragg angle(2θ±0.2°)=27.2° in a CuKα characteristic X-ray diffraction spectrum andone peak in a temperature range from 270 to 400° C. other than the peakderived from vaporization of adsorbed water in differential scanningcalorimetric analysis, the oxo-titanylphthalocyanine crystal beingproduced by a production method comprising the following steps (a) to(d): (a) a step of dissolving a crude oxo-titanylphthalocyanine crystalin an acid to obtain an oxo-titanylphthalocyanine solution; (b) a stepof adding the oxo-titanylphthalocyanine solution dropwise in a poorsolvent to obtain a wet cake; (c) a step of washing the wet cake with analcohol having 1 to 4 carbon atoms; and (d) a step of stirring thewashed wet cake under heating in a nonaqueous solvent to obtain anoxo-titanylphthalocyanine crystal.
 11. The electrophotographicphotoreceptor according to claim 10, wherein the following relationship(1) is established between the reflection absorbance (A/−) of thephotoreceptive layer for light having a wavelength of 700 nm, the filmthickness (d/m) of the photoreceptive layer and the concentration (C/wt%) of the oxo-titanylphthalocyanine crystal in the photoreceptive layer.A·C ⁻¹ ·d ⁻¹>1.75×10⁻⁴  (1)